Female Reproductive System & Ovarian Cycle PDF

Female Reproductive System &Ovarian Cycle  Learning Outcome 1.Identify the structures of the female reproductive system and provide a function for each. 2.List the stages of the ovarian cycle and explain what is occurring in each stage. 3. Describe the process of oogen...

Female Reproductive System &Ovarian Cycle  Learning Outcome 1.Identify the structures of the female reproductive system and provide a function for each. 2.List the stages of the ovarian cycle and explain what is occurring in each stage. 3. Describe the process of oogenesis. 4.Summarize how estrogen and progesterone influence the ovarian cycle  The female reproductive system divided into internal reproductive and external genital organs  Internal reproductive organs Organ --------Function Ovaries------ gonads are paired lie in shallow depressions, one on each side of the upper pelvic cavity. The ovaries produce eggs (technically referred to as ova) and the female sex hormones estrogen and progesterone. Oviducts------ Conduct eggs; location of fertilization(uterine or fallopian tubes) Uterus (womb)------ Houses developing fetus Cervix -------Contains opening to uterus Vagina----- serves as birth canal and as an exit for menstrual flow  The oviducts, also called the uterine or fallopian tubes, extend a projections called fimbriae that sweep over the ovaries. When an egg (ovum) bursts from an ovary during ovulation, it usually is swept into an oviduct by the combined action of the fimbriae and the beating of cilia that line the oviducts.  Once in the oviduct, the egg is propelled slowly by ciliary movement and tubular arrives at the uterus after several days, and then implantation occurs. During implantation, the embryo embeds in the uterine lining, which has been prepared to receive it.  The uterus is a thick-walled, muscular organ about the size and shape of an inverted pear. Normally, it lies above and is tipped over the urinary bladder. The oviducts join the uterus at its upper end; at its lower end, the cervix enters the vagina nearly at a right angle.  Development of the embryo and fetus normally takes place in the uterus, is approximately 5 cm wide in its usual state. It is capable of stretching to over 30 cm wide to accommodate a growing fetus. The lining of the uterus, called the endometrium, participates in the formation of the placenta. The endometrium supplies nutrients needed for embryonic and fetal development. The endometrium has two layers : a functional layer that is shed during each menstrual period and a basal layer of reproducing cells. In the non pregnant female, the functional layer of the endometrium varies in thickness according to a monthly reproductive cycle called the uterine cycle.  A small opening in the cervix leads to the vaginal canal. The vagina is a tube that lies at a 45° angle to the small of the back. The mucosal lining of the vagina lies in folds and can extend. This is especially important when the vagina serves as the birth canal. The vagina also acts as an exit for menstrual flow. Several different types of bacteria normally reside in the vagina and create an acidic environment. This environment is protective against the possible growth of pathogenic bacteria.  :Ovarian Cycle An ovary contains many follicles, and each one contains an immature egg called an oocyte. A female is born with as many as 2 million follicles, but the number is reduced to 300,000 to 400,000 by the time of puberty. Only a small number of follicles (about 400) ever mature because a female usually produces only one egg per month during her reproductive years. As the follicle matures during the ovarian cycle, it changes from a primary to a secondary to a vesicular (Graafian) follicle. Epithelial cells of a primary follicle surround a primary oocyte. Pools of follicular fluid bathe the oocyte in a secondary follicle. In a vesicular follicle, the fluid-filled cavity increases to the point that the follicle wall balloons out on the surface of the ovary  A primary oocyte undergoes meiosis I, and the resulting cells are haploid with 23 chromosomes each. One of these cells is called a polar body. A polar body is a sort of cellular “trash can” because its function is simply to hold discarded chromosomes. The secondary oocyte undergoes meiosis II but only if it is first fertilized by a sperm cell. If the secondary oocyte remains unfertilized, it never completes meiosis and will die shortly after being released from the ovary.  When appropriate, the vesicular follicle bursts, releasing the oocyte (often called an egg) surrounded by a clear membrane. This process is referred to as ovulation. Once a vesicular follicle has lost the oocyte, it develops into a corpus luteum, a glandlike structure. If the egg is not fertilized, the corpus luteum disintegrates. As mentioned previously, the ovaries produce eggs and also the female sex hormones estrogen and progesterone. A primary follicle produces estrogen, and a secondary follicle produces estrogen and some progesterone. The corpus luteum produces progesterone and some estrogen.  Phases of the Ovarian Cycle Similar to the testes, the hypothalamus has ultimate control of the ovaries’ sexual function because it secretes gonadotropin-releasing hormone, or GnRH. GnRH stimulates the anterior pituitary to produce FSH and LH, and these hormones control the ovarian cycle. The gonadotropic hormones are not present in constant amounts. Instead they are secreted at different rates during the cycle.  For simplicity’s sake, it is convenient to emphasize that during the first half, or follicular phase, FSH promotes the development of follicles that primarily secrete estrogen. As the estrogen level in the blood rises, it exerts negative feedback control over the anterior pituitary secretion of FSH. The follicular phase now comes to an end.  The estrogen spike at the end of the follicular phase has a positive feedback effect on the hypothalamus and pituitary gland. As a result, GnRH from the hypothalamus increases. There is a corresponding surge of LH released from the anterior pituitary. The LH surge triggers ovulation at about day 14 of a 28-day cycle. Next, the luteal phase begins. During the luteal phase of the ovarian cycle, LH promotes the development of the corpus luteum. The corpus luteum secretes high levels of progesterone and some estrogen. When pregnancy does not occur, the corpus luteum regresses and a new cycle begins with menstruation.  Estrogen and Progesterone Estrogen and progesterone affect not only the uterus but other parts of the body as well. Estrogen is largely responsible for the secondary sex characteristics in females; axillary and pubic hair during puberty and fat distribution. In general, females have a more rounded appearance than males because of a greater accumulation of fat beneath the skin. Both estrogen and progesterone are also required for breast development. Other hormones are involved in milk production (prolactin) following pregnancy and milk letdown (oxytocin) when a baby begins to nurse.  Menopause, the period in a woman’s life during which the ovarian cycle ceases, is likely to occur between ages 45 and 55. The ovaries are no longer responsive to the gonadotropic hormones produced by the anterior pituitary, and the ovaries no longer secrete estrogen or progesterone. At the onset of menopause, menstruation becomes irregular a woman is usually not considered to have completed menopause until menstruation is absent for 6 month to 1 year.  Uterine Cycle The female sex hormones, estrogen and progesterone, have numerous functions. One function of these hormones affects the endometrium, causing the uterus to undergo a cyclical series of events known as the uterine cycle. Twenty-eight-day cycles are divided as follows: During days 1–5, a low level of estrogen and progesterone in the body causes the endometrium to disintegrate and its blood vessels to rupture. On day 1 of the cycle, a fl ow of blood and tissues, known as the menses, passes out of the vagina during menstruation, also called the menstrual period  During days 6–13, increased production of estrogen by a new ovarian follicle in the ovary causes the endometrium to thicken and become vascular and glandular. This is called the proliferative phase of the uterine cycle. On day 14 of a 28-day cycle, ovulation usually occurs. During days 15–28, increased production of progesterone by the corpus luteum in the ovary causes the endometrium of the uterus to double or triple in thickness (from 1 mm to 2–3 mm). The uterine glands mature and produce a thick mucoid secretion in response to increased progesterone. This is called the secretory phase of the uterine cycle. The endometrium is now prepared to receive the developing embryo. If this does not occur, the corpus luteum in the ovary regresses. The low level of progesterone in the female body results in the endometrium breaking down during menstruation Thank you